In general, no protective door is installed in the current common sockets on the market, namely, jacks are typically exposed. There will be the danger of electric shock if a metal foreign substance, e.g. a key, is inserted into jacks by children.
Some sockets with protective door have been commercially available to avoid this kind of dangerous accident, and jacks are opened by poking manually when these sockets are in use and are covered when not in use, so unsafe factors still exist; and in some other sockets with protective doors, the protective door opens or closes the jacks only by means of a spring-pushing elastic force because the protective door has no limiting function. As a result, the insertion of foreign impurities into single jack cannot be prevented effectively, which also causes potential danger.